The present invention relates generally to an oven for heating, cooking and baking food products and more particularly to a hot air type oven having cooking characteristics similar to those of a hearth type oven.
Certain conveyorized hot air ovens have been used successfully for a number of years to quickly cook food products, particularly pizza, within a relatively short travel path, on the order of three to five feet. A particularly advantageous arrangement for such conveyor ovens involves impingement cooking wherein standing columns of hot air are directed at localized areas of the moving food product to cook the food product and to carry away moisture and particles resulting from the cooking process. The above cooking process involves extremely efficient convection heating of the food product wherein the high velocity, highly turbulent columns of hot air impart a large amount of heat energy into the food product in a short amount of time. Depending on the dough mixture, such impingement heating of pizza dough may result in some "chalking" of the crust and a slight change of flavor as compared to a hearth oven baked pizza because the impingement energy sets up the exterior of the crust before thorough crust development can happen. In addition, it is difficult to make the crust "crisp" with convection or impingement heating.
A significant portion of the pizza market requires a pizza product having a crust which is crispy and a golden color on the bottom. Such a crust texture is characteristic of pizzas cooked in a traditional hearth type pizza oven in which the pizza is laid on a solid hot surface composed of a metallic or ceramic material. Contrary to what one might initially suppose, it is believed that the crispy bottom surface of pizza crust which is obtained in a hearth oven is not solely the result of conduction heating of the dough by the hot surface of the hearth. Although pizza dough in a hearth oven is in intimate contact with the hearth surface, a thin layer of water vapor formed during cooking acts as insulation and prevents total transfer of heat to the pizza dough via conduction. It is believed that the crispy nature of the bottom of the pizza crust cooked on a hearth is additionally the result of heating of the dough by infra-red radiation emitted from the hot hearth surface.
It would be desirable to provide a hot air type oven with its inherent speed and efficiency characteristics which would also cook pizza crust so as to have a crispy bottom surface in the nature of a hearth-baked pizza. An oven constructed in accordance with the present invention provides such desired characteristics.
U.S. Pat. No. 4,462,383 discloses an impingement oven for preparing foods wherein duct fingers are provided, with each finger having a jet plate through which hot air is vented outwardly in standing columns to impinge on food products located between the duct fingers in an oven cavity. The food travels on a conveyor belt between the duct fingers as it is being cooked. The oven incorporates a fan and plenum system whose high pressure side is connected to both upper and lower duct fingers whereby hot air impinges downwardly from the upper duct fingers and upwardly from the lower duct fingers simultaneously onto the respective sides of the food product. The fan recirculates the air within the oven cavity for reheating and subsequent passage through the plenum and duct fingers.
U.S. Pat. No. 4,626,661 discloses an air delivery system for an impingement food preparation oven wherein the fan blades and plenum are configured for smoother flow of heated air from the fan through the plenum.
U.S. Pat. No. 4,591,333 discloses an impingement oven which includes radiant panels positioned above the conveyor to impart heat to the food product by means of infra-red radiation. In one embodiment, the hot air apertures of conventional impingement duct fingers are covered by highly thermally conductive radiant energy plates upon which the hot air impinges, and which deflect the impinging air laterally and upwardly away from the food product. The plates include an emissive outer surface which when the panel becomes heated by impingement of hot air thereon, radiates infra-red energy toward the food product. In a second embodiment, the apertured radiant plate of the impingement finger is replaced by a solid emissive panel having corner apertures to permit pressurized air to escape the duct and be drawn back into the plenum.
U.S. Pat. Nos. 4,462,383, 4,626,661 and 4,591,333 are hereby incorporated by reference.